Optoelectric sensors, which can convert optical signals (e.g. infrared, visible and ultraviolet radiation) into electrical signals, are key elements to achieve photon to electricity conversion in various detecting systems, such as fingerprint sensor. Fingerprint identification, as one kind of biometric identification, has attracted widespread attention recently, especially in mobile payment applications.
In an existed optical fingerprint identification sensor, a CMOS (Complementary Metal Oxide Semiconductor) or CCD (Charge-Coupled Device) imaging sensor array is applied to collect optical signals for fingerprint detection.
Referring to FIG. 1, one optical fingerprint identification sensor that applies CMOS imaging array is illustrated. The fingerprint sensor generally includes a CMOS imaging sensor array 01, an optical fiber array 02, and a light source 03. The optical fiber array 02 is an array that includes small-dimension optical fiber bundles, with the light source 03 located on one side. In a fingerprint identification process, a finger 05 contacted with the top end of the optical fiber array 02, lights of the light source 03 pass through the optical fiber array 02 and be reflected at the bottom part of the finger 05. The reflected lights then penetrate through the optical fiber array 02 to reach the CMOS imaging sensor array 01 in which pixel cells are disposed. Skin surface of finger 05 closely contacts to the top end of the optical fiber array 02, therefore the lights reflected by the ridge may have higher light intensity. Lights reflected by the valley may have lower light intensity. Therefore, light received by the pixel cells of the CMOS imaging sensor array 01 are different. The CMOS imaging sensor can convert optical signals of different light intensity into electrical signals, such that the information of the fingerprint surface can be obtained.
The optical fiber array 02 is used to partition the lights reflected by different parts of the bottom of the finger 05 and transmit them into different pixel cells in the CMOS imaging sensor array. However, since the pixel cells of the CMOS imaging sensor array have complicated structures and inadequate signal range to the reflected light, the contrast between the reflected lights of the ridge and valley is limited. Currently, an angle is defined between the light bundles of the optical fiber array 02 and one top end surface of the optical fiber array 02, so as to ensure that most of the reflected lights of the valley can not enter into the optical fiber array 02. Accordingly, the optical fiber array 02 is purposely configured to have a bended shape as shown in FIG. 1, while the CMOS imaging sensor array 01 is fixed on the other end of the optical fiber array 02, which top end surface is perpendicular to the optical fiber array 02. Although, it can be seen that the bended shape of the optical fiber array increases the size of the fingerprint identification area that can be detected by CMOS imaging sensor array, the whole fingerprint identification system will be difficult to be integrated into portable devices such as mobile phones. Furthermore, the light source 03 is located at one side of the optical fiber array 02, thus the light intensity received by different portions of the finger 05 are different from each other. Lights received by bottom portions with longer distance from the light source 03 may have lower light intensity, which makes the CMOS imaging sensor array 01 have poor uniformity.
Furthermore, the traditional optoelectric finger print sensors which require lenses may not be easily integrated into mobile devices, especially under the requirement of high resolution or the limitation of geometry.
Most of the currently existing finger print sensors such as capacitance type can only achieve single function. Products that can bring multifunction as well as being compact enough to fit into portable devices can bring benefit to the consumers and save cost for the manufactures.